Conventionally, dyes have been widely used in various technical fields. As one example, in the field of photoelectric conversion devices, for example, a dye having photosensitization action is used in the working electrode of a dye-sensitized solar cell.
A dye-sensitized solar cell generally has an electrode having an oxide semiconductor as a support for a dye. Such a dye absorbs incident light and is excited, and this excited dye injects electrons into the support to perform photoelectric conversion. In this type of dye-sensitized solar cell, high energy conversion efficiency can be theoretically expected among organic solar cells. In addition, this type of dye-sensitized solar cell can be produced at lower cost than conventional solar cells using a silicon semiconductor, and therefore is considered to be very advantageous in terms of cost.
On the other hand, as dyes used in photoelectric conversion devices, organic dyes, such as ruthenium complex dyes and cyanine dyes, are widely known. Particularly, cyanine dyes have relatively high stability, and can be easily synthesized, and therefore, various studies have been made.
For example, Patent Document 1 discloses a cyanine dye that has a structure in which an indolenine skeleton is bonded to both ends of a methine chain skeleton, and further has a carboxylic acid group as an anchor group to be adsorbed on an oxide semiconductor electrode.
In addition, Patent Document 2 discloses a composite dye in which a plurality of component dyes having different excitation levels from each other are chemically bonded to each other, thereby forming a linear or branched structure for electron transfer, the linear or branched structure is held at one end by an n-type semiconductor, the other end is a free end, and in the linear or branched structure, the plurality of component dyes are arranged in the order in which the excitation level decreases from the end of the linear or branched structure held by the above n-type semiconductor toward the above free end.
Further, Patent Document 3 discloses a sensitizing dye in which a dye having an absorption maximum at 400 to 700 nm is bonded to a dye having an absorption maximum at 700 to 1500 nm by a divalent linking group.